This invention relates to thermal-image sensing devices comprising a 2-dimensional array of ferroelectric or pyroelectric infrared detector elements, and further relates to methods of manufacturing such devices.
Published European patent application EP-A-0 173 368 discloses a method of manufacturing a thermal-image sensing device comprising a 2-dimensional array of ferroelectric or pyroelectric infrared detector elements which are mounted on a circuit substrate via an intermediate layer of thermally and electrically insulating material. In this method a corresponding 2-dimensional array of bores is formed in the insulating layer, and each of the detector elements is electrically connected to a respective electrode of the circuit substrate by means of a metal coating over the wall of its respective bore. This electrical connection restricted in cross-section to the thin metal coating provides a low thermal conductive path between the detector elements and the circuit substrate. The whole contents of EP-A-0 173 368 are hereby incorporated as reference material in the present specification.
In the particular method described in EP-A-0 173 368, after forming the detector element array, the insulating layer in the form of a sheet is bonded to a signal electrode layer on one major surface of the detector element array, the bores are etched through the insulating sheet to the signal electrode layer and metallized, and a pattern of grooves (channels) are then etched through the insulating sheet to the detector element array so as to form pillars each surrounding a respective bore. The bores and grooves need to be aligned with respect to the detector element array. This sub-assembly of the metallized insulating pillar structure and detector element array is then carefully mounted on the circuit substrate by means of solder bumps on the corresponding electrodes of the circuit substrate.
This particular method provides a device structure in which the intermediate insulating layer is spaced away from the upper surface of the substrate by the solder bumps and is divided into separate pillars throughout its thickness. This permits the use of insulating layer materials such as cadmium telluride, tellurium, selenium or sulphur, having only moderate insulation properties. An advantage of using these materials is that the bores can be formed by milling with an ion beam at windows in a photoresist coating.